For a large and complex shaped TA15 titanium alloy forging,the content of primary α phase generally changes with the size of the different sections and would significantly affects the mechanical properties whenever at the room temperature and high temperature. The relationship of the content of primary α phase and tensile strength at the room temperature and 500 ℃ was measured and realized in the paper. In order to control the α phase content,the influences of the forging process parameters on the content of α phase were systematically studied. The parameters included heating temperature,cooling way,section thickness and heating times within the selectable process window.The result shows that α phase content decreases with the increase of heating temperature and cooling rate,heating times,and also decreases with the thinning of the sample thickness and vice versa. Finally,the equations were obtained for calculating the content of the α phase resulted from the forging process parameters. Various factors on αphase content should be considered when we make a process route to fabricate a large forging. Therefore,to meet the requirement of the in-serve performance,primary α content control could be feasible relying on the relationship between the proportion of α phase and the mechanical properties.